If the departure from CDG existed, why would it be taken from the schedule even if it was full? Why not just show "sold out" or similar notation? People already on the train could well be checking times of departure, etc.

I have run into situations in France where a train was listed on the SNCF schedule and then failed to show at the station at the appointed time.

I remember very clearly one night in Melun when we were trying to return to Paris after the candlelight night at Vaux le Vicomte. Not there. I had to take another train that took twice as long.

There are two ways to search on the SNCF site. One is for schedules and the other is to buy tickets. If you search to buy tickets it will only show available trains not unlike when you search for plane tickets. If you want to see the schedule, you need to select "timetable". The 21h37 train only runs on certain days.